1. Field of the Invention
The present invention relates to an orientation control apparatus for controlling the orientation of a space vehicle, such as an artificial satellite.
2. Description of the Related Art
In general, an artificial satellite is equipped with an antenna. With this antenna, the satellite body is controlled such that it maintains a predetermined orientation with reference to the Earth, and simultaneously, the antenna of the satellite is controlled such that it is directed toward an Earth station or toward a certain target object (e.g., another artificial satellite). (The latter control should be referred to accurately as directivity control, but the directivity control will be described herein as one of orientation controls, for the purpose of simplicity.) If the orientation of the satellite body is varied, the orientation of the antenna is also varied, accordingly. Conversely, if the orientation of the antenna is varied, the orientation of the main body is also varied, due to the dynamic effects caused by the antenna orientation control. In a conventional orientation control apparatus, therefore, the control band of an antenna orientation control system is kept sufficiently apart from that of a satellite body orientation control system, in order that the antenna orientation control system does not interfere with the satellite body orientation control system due to the dynamic effects. This measure is taken not only for the antenna orientation control system but also for the orientation control system for another device provided for the satellite, e.g., a solar paddle. Further, a similar measure is taken in another type of space vehicles, such as a space station.
It is difficult to provide a large-sized device for a space vehicle, if the device requires orientation control. In recent years, there is a tendency to launch larger satellites than before. In accordance with this tendency, larger antennas have come to be employed for the satellites. If the antenna employed for a satellite is large, the driving mechanism for the antenna must naturally output a large driving force. If the driving force is large, the dynamic effects acting on the satellite body inevitably increase. In addition, the unnecessary power consumption in the driving mechanism increases. Therefore, there are many restrictions regarding the employment of a large-sized antenna, and the orientation control system used for such an antenna must be designed and manufactured in consideration of the restrictions. In the prior art, therefore, it is difficult to employ a large-sized antenna for a space vehicle.